A fastening device of the above-cited type was described by the applicant in patent application EP 2 229 836. As is presented in that document, simple attachment and detachment of wrist straps to/from a case, in particular in conjunction with watch straps is desirable or necessary in everyday life in a large number of situations. The solution presented in that document for a fastening device for an exchangeable wrist strap, in particular in the watch sector, the device being of relatively simple design and simultaneously functioning without additional tools, provided a considerable improvement with regard to these devices. Over the course of further adaptation and development of the use of the system, however, the applicant encountered difficulties which were not discernible at the start.
On the one hand, the use of the fastening device described in patent application EP 2 229 836 for exchanging a wrist strap initially requires two movements in translation, to be carried out in succession and directed in different directions, of the entire device relative to the case to which the device is to be fastened, followed by a rotational movement of the device relative to the casing. This may be found to be complicated or bothersome by unpracticed users or with infrequent actuation, and it therefore appears to be worthwhile simplifying the course of the movement and thereby changing the structure of the device forming the basis of this course of movement.
On the other hand, in the case of the above-mentioned device, a small flattened region or a notch is required laterally on the watch case, for example with use in the watch sector, as is schematically clear from the figures of patent application EP 2 229 836. This is the case in particular insofar as the shaft of the securing element used in this device is attached relatively closely to the case-side end of the fastening device. Due to the normally round shape of watch cases, the shaft therefore would stand in the way of the watch case in the central part of the device if the watch case were not provided at this point with the flattened region or a notch. In order to overcome this design limitation, no matter how slight, at the case, a fastening device which is also improved in this regard therefore is desirable.
In any case, the improved fastening device for an exchangeable wrist strap without use of tools should also satisfy the criteria with regard to aesthetics, ergonomics, wearer comfort, hygiene by way of simple cleaning of the system and, in particular, robustness and protection against accidental detachment, as is the case with the device according to patent application EP 2 229 836. It should also be possible to use the device with any type of exchangeable wrist straps, that is to say not only in relation to watches, but generally with any type of wrist strap which is mounted onto a case and has to be occasionally exchanged.